The proposed research will investigate the role of bovine mammary secretory cell membranes in calcium metabolism. These studies will establish the calcium distribution and calcium flux in the bovine mammary secretory cell, with particular emphasis on the role of plasma membrane, mitochondria, and Golgi apparatus in this process. The subcellular distribution of calcium will be examined during the course of lactogenesis and possible lactogenic factors that influence this distribution will be explored. Such studies may suggest the involvement of cellular components heretofore unsuspected. Evidence currently available implicates the previous mentioned cellular fractions, each of which will be investigated in the course of these studies. In view of the high concentration of calcium in milk, the flux across the epithelial mammary cells must increase dramatically with the onset of lactation. The mode of transport across the plasma membrane will be investigated, as well as factors that may trigger this increase. Golgi apparatus will be studied for its role in the export of calcium into milk. A Ca 2 ion-stimulated ATPase from the Golgi apparatus will be explored as to its mechanism and its interaction with casein and lactose secretion. The answers to be obtained will elucidate the metabolism of calcium in lactating mammary cells. These answers are highly significant in light of the present U.S. diet dependancy upon milk as a primary source of calcium.